Thermal denaturation of UV-irradiated wet rat tail tendon collagen

The thermal helix-coil transition of UV irradiated collagen in rat tail tendon has been investigated by differential scanning calorimetry. During UVB irradiation the tendons were immersed in water to keep the collagen fibers in a fully hydrated condition at all times. UV irradiation induced changes in collagen which caused both stabilization and destabilization of the triple helix in fibers. The helix-coil transition for non-irradiated collagen occurred near 64 degrees C, for irradiated 1 and 3 h at 66 and 67 degrees C, respectively. After irradiating for longer times (20-66 h) the helix-coil transition peak occurred at much lower temperatures. The peak was very broad and suggested that collagen was reduced by UV to different polypeptides of different molecular weight and different lower thermal stabilities. It was caused by the disruption of a network of hydrogen-bonded water molecules surrounding the collagen macromolecule.     

Metallo-protease activity increases prior to ovulation in brook trout (Salvelinus fontinalis) and yellow perch (Perca flavescens) follicle walls

Proteolytic activity was measured in the follicle wall surrounding oocytes from brook trout (Salvelinus fontinalis) and yellow perch (Perca flavescens) by use of two different protease assays: sodium dodecyl sulfate-polyacrylamide gel electrophoresis (substrate-SDS-PAGE) and a chromogenic synthetic peptide for type I collagen. In brook trout follicle walls, substrate-SDS-PAGE studies demonstrated that the activity of two proteolytic enzymes (80 kDa and 66 kDa) increased significantly before ovulation. The 80 kDa enzyme decreased significantly after ovulation whereas the 66 kDa enzyme remained elevated following ovulation. In yellow perch follicle walls, substrate-SDS-PAGE studies demonstrated that the activity of the major protease (66 kDa) increased before ovulation and remained elevated after ovulation. A chromogenic synthetic peptide was used to assay collagenolytic activity in follicle walls of brook trout and yellow perch. This assay revealed that collagenolytic activity increased significantly in both species before ovulation and remained elevated after ovulation. These findings suggest that metallo-proteases are involved in digesting the follicle wall in teleosts before and after ovulation.     

Motility and fertility of equine spermatozoa in a milk extender after 12 or 24 hours at 20 degrees C

The effects of extender and storage at 20 degrees C on equine spermatozoa were evaluated in two experiments using embryo recovery as the end point. In both experiments, inseminations were every other day, starting on Day 2 or 3 of estrus or after a 35-mm follicle was detected, with 250 x 10(6) progressively motile cells (based on initial evaluation). In Experiment 1, semen from two stallions was used to compare the motility and fertility of spermatozoa maintained in a) heated skim milk extender at 37 degrees C with insemination in <1 h; b) E-Z Mixin extender at 37 degrees C with insemination in <1 h; and c) E-Z Mixin extender at 37 degrees C with cooling to 20 degrees C and insemination after storage for 12 h at 20 degrees C. The percentage of motile spermatozoa was 34% after 12 h compared to 55% at 0 h (P < 0.05). However, the percentage of mares from which an embryo was recovered 6.5 d after ovulation was 62, 56, and 50% for Treatments A, B, and C (P > 0.05). In Experiment 2, semen from three stallions was used to compare the motility and fertility of spermatozoa in a) E-Z Mixin extender at 37 degrees C with insemination in <1 h or b) E-Z Mixin extender at 37 degrees C with cooling to 20 degrees C and insemination after storage for 24 h at 20 degrees C. The percentage of motile spermatozoa was 17% after 24 h compared to 54% at 0 h (P < 0.05). There was no difference between treatments (P > 0.05) in the percentage of mares from which an embryo was recovered 6.0 d after ovulation (68 vs 62%) or among stallions. Thus, stallion semen extended in E-Z Mixin was held at 20 degrees C for 24 h without a marked decline in fertility.     

In vitro maturation and transfer of equine oocytes after transport of ovaries at 12 or 22 degrees C

Transportation of equine ovaries would allow shipment of oocytes for research purposes or transfer after the death of a valuable mare. The objective of this study was to compare two temperatures for maintaining ovaries during a transport interval of 18-24 h. The goal was to obtain pregnancies after transport of ovaries, maturation of oocytes in vitro, and transfer of oocytes. Each shipment was composed of ovaries four to seven mares collected from an abattoir. From each mare, one ovary was packaged at approximately 12 degrees C, and the other was packaged at approximately 22 degrees C. Upon arrival at our laboratory, oocytes were collected and cultured for 24 h. For each transfer, between 9 and 15 oocytes from each group were placed into the oviducts of estrous mares through standing flank laparotomies. Recipients received human chorionic gonadotropin (hCG; 2000 IU, i.v.) 30-36 h before transfer (to synchronize ovulation). Recipients were inseminated 18-20 h before transfers with 2 x 10(9) progressively motile sperm. Uteri of recipients were examined with ultrasound to determine the number of developing embryos. On Day 16 ( ovulation = day 0), developing embryos were recovered by uterine lavage. Parentage verification was performed on recovered vesicles. Pregnancy rates were analyzed by Chi-square. The percentage of oocytes that developed into embryonic vesicles on Day 16 was not different between transport temperatures (22 degrees C, 13/73, 18% versus 12 degrees C, 11/73, 15%). In conclusion, pregnancies were obtained from in vitro matured oocytes that were recovered from ovaries transported for 18-24h at 12 or 22 degrees C.     

The extraction of a tissue collagenase associated with ovulation in the rat

A method has been developed to assay collagenase in ovarian extracts in the presence of tissue inhibitors. Rat ovarian tissue is first extracted with Triton X-100 and then heated to 60 degrees C in 50 mM Tris buffer containing 100 mM CaCl2. This extract contains collagenase activity and putative inhibitor(s). The inhibitory activity is removed by reduction with dithiothreitol and alkylation with iodoacetamide. Collagenase is then activated with aminophenylmercuric acetate and assayed using 3H-acetylated collagen from which the telopeptides have been removed. Identification of this activity as collagenase was performed by using the metalloprotease inhibitors EDTA and o-phenanthroline and by demonstration of the typical collagen cleavage fragments on sodium dodecyl sulfate-gel electrophoresis. To investigate the changes in collagenase activity associated with ovulation, immature rats received 20 IU of pregnant mare's serum gonadotropin and 52 h later 10 IU of human chorionic gonadotropin (hCG). After hCG administration, ovaries were removed at intervals from 0 to 20 h. Collagenase activity rose from 4.9 +/- 1.4% digestion of the 3H-collagen at 0 time to a maximum of 24.7 +/- 1.5% digestion at 8 h after hCG and remained high at 12 h (time of ovulation) and up to 20 h (18.7 +/- 1.9% and 16.1 +/- 1.6% digestion, respectively). These findings support a role of collagenase in the rupture of the follicle and they suggest a further role for this enzyme in the events following ovulation.     

Fertility of cooled and frozen rabbit sperm measured by competitive fertilization

The fertility of rabbit sperm that had been cooled to 5 degrees C or frozen and thawed was determined by competitive fertilization. Treatments were identified by labeling sperm with fluorescein isothiocyanate (FITC) or tetramethylrhodamine B isothiocyanate (TRITC). Sperm from different treatments were mixed and used in a competitive insemination experiment. Does were inseminated 5, 10 or 15 h prior to ovulation. Time of ovulation was controlled by injections of luteinizing hormone. The functional sperm transport, as determined by the number of sperm transported to the site of fertilization and capable of fertilizing oocytes, was estimated by counting the total number of differently stained sperm that surrounded or fertilized each oocyte. The fertility of sperm cooled to 5 degrees C was not affected (p less than 0.05) as compared to fertility of uncooled sperm. Functional sperm transport at all times of insemination and fertilization ratio at insemination 10 or 15 h before ovulation were reduced (p less than 0.05) for frozen-thawed vs. cooled sperm. No difference in fertilization ratio (p greater than 0.05) occurred, however, when does were inseminated 5 h before ovulation. While sperm survival and capacitation time appeared to play roles in fertility of frozen-thawed sperm, the most important factor was reduced functional sperm transport. However, fertility of frozen-thawed sperm was improved when the time from insemination to ovulation was reduced.     

Relationship between progesterone concentrations in milk and blood and time of ovulation in dairy cattle

The objective of this study was to investigate whether monitoring progesterone concentrations in milk and blood plasma can be used to predict time of ovulation in dairy cattle. Whole milk was sampled twice daily and blood samples were collected once a day before the morning milking. Ovulation was assessed by trans-rectal ultrasonography at 4h intervals beginning from the end of estrus. For a parameter to be useful as predictor for time of ovulation, it should be precise (i.e. variation between animals should not exceed 12h). In milk, progesterone concentration dropped <15 ng/ml at 97.7+/-17.8h (range: 54-126 h) before ovulation, to <5 ng/ml at 79.7+/-11.2h (range: 54-98) before ovulation to decline further to <2n g/ml at 70.7+/-16.8h (range: 38-90 h) before ovulation (n=20). In plasma, progesterone concentration dropped to <4ng/ml 90.5+/-19.6h (range: 66-138 h) before ovulation and to <2 ng/ml at 75.0+/-12.2 h (range: 50-98) before ovulation. These intervals were not influenced by parity, milk production or days in milk. In conclusion, monitoring of progesterone alone is not sufficient to predict ovulation because of the large variation in timing of decrease of progesterone concentrations relative to ovulation between animals. At best the range is about 2 days.     

Temperature induced denaturation of collagen in acidic solution

The denaturation of collagen solution in acetic acid has been investigated by using ultra-sensitive differential scanning calorimetry (US-DSC), circular dichroism (CD), and laser light scattering (LLS). US-DSC measurements reveal that the collagen exhibits a bimodal transition, i.e., there exists a shoulder transition before the major transition. Such a shoulder transition can recover from a cooling when the collagen is heated to a temperature below 35 degrees C. However, when the heating temperature is above 37 degrees C, both the shoulder and major transitions are irreversible. CD measurements demonstrate the content of triple helix slowly decreases with temperature at a temperature below 35 degrees C, but it drastically decreases at a higher temperature. Our experiments suggest that the shoulder transition and major transition arise from the defibrillation and denaturation of collagen, respectively. LLS measurements show the average hydrodynamic radius R(h), radius of gyration R(g)of the collagen gradually decrease before a sharp decrease at a higher temperature. Meanwhile, the ratio R(g)/R(h) gradually increases at a temperature below approximately 34 degrees C and drastically increases in the range 34-40 degrees C, further indicating the defibrillation of collagen before the denaturation.     

Short-term storage of oocytes from the neotropical teleost fish Prochilodus marggravii

The loss of oocyte viability after ovulation is one of the limiting factors in controlled reproduction of several fish species. Experiments were performed with 15 feral Prochilodus marggravii female fish induced to spawn with crude carp pituitary extract to evaluate the viability of oocytes retained within the ovarian cavity (in situ storage) and outside of the ovarian cavity (ex situ storage). Because fertility rates rapidly declined after ovulation, simultaneously with an increase in the number of deformed larvae, P. marggravii oocytes could only be successfully stored for 1 h ex situ at room temperature ( approximately 26 degrees C). There was a highly negative correlation (r = -0.82) between fertilization and deformed larvae during in situ storage at approximately 26 degrees C. Ex situ cooling (18 degrees C) caused a drastic reduction in fertilization rates as compared with storage at approximately 26 degrees C. Oocyte structure was preserved during 2 h storage and the cortical reaction was induced before spawning. Since the micropylar apparatus remained open, it was not the primary cause for the loss of oocyte fertility. The cytoskeleton of the oocyte appeared to be affected since ooplasmic segregation was altered after 2 h storage.     

The influence of water removal on the strength and toughness of cortical bone

Although the effects of dehydration on the mechanical behavior of cortical bone are known, the underlying mechanisms for such effects are not clear. We hypothesize that the interactions of water with the collagen and mineral phases each have a unique influence on mechanical behavior. To study this, strength, toughness, and stiffness were measured with three-point bend specimens made from the mid-diaphysis of human cadaveric femurs and divided into six test groups: control (hydrated), drying in a vacuum oven at room temperature (21 degrees C) for 30 min and at 21, 50, 70, or 110 degrees C for 4 h. The experimental data indicated that water loss significantly increased with each increase in drying condition. Bone strength increased with a 5% loss of water by weight, which was caused by drying at 21 degrees C for 4 h. With water loss exceeding 9%, caused by higher drying temperatures (> or =70 degrees C), strength actually decreased. Drying at 21 degrees C (irrespective of time in vacuum) significantly decreased bone toughness through a loss of plasticity. However, drying at 70 degrees C and above caused toughness to decrease through decreases in strength and fracture strain. Stiffness linearly increased with an increase in water loss. From an energy perspective, the water-mineral interaction is removed at higher temperatures than the water-collagen interaction. Therefore, we speculate that loss of water in the collagen phase decreases the toughness of bone, whereas loss of water associated with the mineral phase decreases both bone strength and toughness.     

Conformational stability of type I collagen triple helix: evidence for temporary and local relaxation of the protein conformation using a proteolytic probe

Native collagen polypeptides exist in a unique triple helical conformation resistant to most proteinases. In this study, the stability of type I collagen triple helix, employing a mixture of trypsin and alpha-chymotrypsin as a proteolytic probe, was examined. The degradation of type I [3H]collagen was monitored as 3H-labeled peptides soluble in trichloroacetic acid (TCA) or by sodium dodecyl sulfate (SDS)-polyacrylamide slab gel electrophoresis. In one set of experiments, collagen substrates were preincubated at various temperatures for up to 8 h, followed by a 15-min proteolytic treatment at the same temperature. At 43 degrees C, most of the collagen was degraded, while the fraction of the substrate degraded at 40, 38, and 35 degrees C was 53, 41 and 19%, respectively. This fraction was independent of the preincubation time which varied from 10 to 480 min. Thus, at any given temperature, a constant fraction of the collagen substrate was susceptible to proteolysis. Measurement of the midpoint temperature (Tm) of the helix to coil transformation for type I collagen, at neutral pH employing an increasing temperature gradient and brief proteolysis at the individual temperatures, indicated a value of 38.8 degrees C. However, determination of the Tm by employing proteolytic digestions at a constant temperature (30 degrees C) using conditions under which the nonhelical peptides are readily digested to TCA-soluble peptides while native collagen resists such proteolysis, indicated a value of 42.7 degrees C. In further studies, collagen was subjected to continuous proteolysis for up to 24 h. A large fraction of collagen was digested at 30 or 34 degrees C, temperatures well below the Tm of the helix to coil transformation. SDS-polyacrylamide gel electrophoresis of the degradation products obtained at these temperatures revealed multiple cleavage fragments. Finally, temperature double-jump experiments indicated that the destabilization of the triple helix is reversible provided that the Tm of the substrate is not exceeded. The results provide evidence for reversible and local relaxation of the collagen triple helix.     

Effect of high compost temperature on enzymatic activity and species diversity of culturable bacteria in cattle manure compost

To clarify the characteristics of thermophilic bacteria in cattle manure compost, enzymatic activity and species diversity of cultivated bacteria were investigated at 54, 60, 63, 66 and 70 degrees C, which were dependent on composting temperature. The highest level of thermophilic bacterial activity was observed at 54 degrees C. Following an increase in temperature to 63 degrees C, a reduction in bacterial diversity was observed. At 66 degrees C, bacterial diversity increased again, and diverse bacteria including Thermus spp. and thermophilic Bacillus spp. appeared to adapt to the higher temperature. At 70 degrees C, bacterial activity measured as superoxide dismutase and catalase activity was significantly higher than at 66 degrees C. However, the decomposition rate of protein in the compost was lower than the rate at 66 degrees C due to the higher compost temperature.     

Ovulatory response, and plasma concentrations of luteinizing hormone and progesterone following administration of synthetic mammalian or chicken luteinizing hormone-releasing hormone relative to the first or second ovulation in the sequence of the domestic hen

Experiments were conducted to investigate hypophyseal and follicular competency at two distinct stages of the hen's egg laying sequence: 1) 14 h prior to the first (C1) ovulation of a sequence (27 h following the previous ovulation); and 2) 14 h prior to the second (C2) ovulation of a sequence (13 h following the previous ovulation). When a single dose of mammalian luteinizing hormone-releasing hormone (mLHRH) or chicken luteinizing hormone-releasing hormone (cLHRH) was injected 14 h prior to a C1 ovulation, premature ovulation was induced in 19 of 20 hens. In contrast, ovulation was premature in only 1 of 20 hens when mLHRH or cLHRH was injected 14 h prior to a C2 ovulation. There was no difference between the two stages of the sequence in the amount of luteinizing hormone (LH) released for up to 60 min following a single i.v. injection of 20 micrograms mLHRH. However, only prior to a C1 ovulation did LH levels further increase to reach preovulatory concentrations. By contrast, progesterone (P4) concentrations were increased within the first 60 min to a lesser extent in hens injected prior to a C2 ovulation compared to a C1 ovulation. In C2-injected birds, P4 fell to levels that were not different from vehicle-injected controls by 45 to 60 min following injection, whereas P4 secretion was maintained in hens injected prior to a C1 ovulation. We suggest that the lack of sustained LH secretion following treatment with either species of LHRH 14 h prior to a C2 ovulation is related to follicular immaturity with respect to ability to produce and secrete P4. At the dosage administered, there was no difference in the ability of mLHRH compared to cLHRH to release LH at either stage of the sequence. Finally, two successive injections of mLHRH at 14 and 13 h prior to a C2 ovulation induced premature ovulation in 6 of 11 hens. It is suggested that LH, and possibly P4, exerts a priming effect on the largest preovulatory follicle to initiate fully potentiated P4 production and secretion.     

Comparative analysis of the structure and thermal stability of sea urchin peristome and rat tail tendon collagen

We have purified collagen from two distinct sources; the vertebrate, rat tail tendon and an invertebrate, sea urchin adult tissue, the peristome. The collagenous nature of the purification products was confirmed by amino acid compositional analysis. Both preparations had high contents of glycine and proline residues and hydroxyproline was also present. The total pyrrolidine (proline+hydroxyproline) content decreased from 17.9 mole% in rat tail collagen to 12.9 mole% in peristome collagen. Distinctly different circular dichroic spectra were measured for these collagens. Analyses of spectra, measured as a function of temperature, revealed distinct thermal denaturation profiles. The melting temperature for rat tail collagen was 38.5 degrees C, while the corresponding value for peristome collagen was significantly lower at 27 degrees C. A similar thermal denaturation profile was obtained for rat tail collagen in digestion experiments using a 41-kDa gelatinase activity, isolated from sea urchin eggs. These results identify structural differences between a typical, vertebrate type I fibrillar collagen and an echinoderm collagen which serves as a constituent of a mutable connective tissue. These differences may relate to the functional roles played by collagen in these distinctly different tissues.     

Susceptibility of cartilage collagens type II, IX, X, and XI to human synovial collagenase and neutrophil elastase

The action of purified rheumatoid synovial collagenase and human neutrophil elastase on the cartilage collagen types II, IX, X and XI was examined. At 25 degrees C, collagenase attacked type II and type X (45-kDa pepsin-solubilized) collagens to produce specific products reflecting one and at least two cleavages respectively. At 35 degrees C, collagenase completely degraded the type II collagen molecule to small peptides whereas a large fragment of the type X molecule was resistant to further degradation. In contrast, collagen type IX (native, intact and pepsin-solubilized type M) and collagen type XI were resistant to collagenase attack at both 25 degrees C and 35 degrees C even in the presence of excess enzyme. Mixtures of type II collagen with equimolar amounts of either type IX or XI did not affect the rate at which the former was degraded by collagenase at 25 degrees C. Purified neutrophil elastase, shown to be functionally active against soluble type III collagen, had no effect on collagen type II at 25 degrees C or 35 degrees C. At 25 degrees C collagen types IX (pepsin-solubilized type M) and XI were also resistant to elastase, but at 35 degrees C both were susceptible to degradation with type IX being reduced to very small peptides. Collagen type X (45-kDa pepsin-solubilized) was susceptible to elastase attack at 25 degrees C and 35 degrees C as judged by the production of specific products that corresponded closely with those produced by collagenase. Although synovial collagenase failed to degrade collagen types IX and XI, all the cartilage collagen species examined were degraded at 35 degrees C by conditioned culture medium from IL1-activated human articular chondrocytes. Thus chondrocytes have the potential to catabolise each cartilage collagen species, but the specificity and number of the chondrocyte-derived collagenase(s) has yet to be resolved.     

Assembly of collagen fibrils de novo by cleavage of the type I pC-collagen with procollagen C-proteinase. Assay of critical concentration demonstrates that collagen self-assembly is a classical example of an entropy-driven process

Type I procollagen was purified from the medium of cultured human fibroblasts incubated with 14C-labeled amino acids, the NH2-terminal propeptides were cleaved with procollagen N-proteinase, and the resulting pC-collagen was isolated by gel filtration chromatography. pC-collagen did not assemble into fibrils or large aggregates even at concentrations of 0.5 mg.ml-1 at 34 degrees C in a physiological buffer. However, cleavage of pC-collagen to collagen with purified C-proteinase (Hojima, Y., (1985) J. Biol. Chem. 260, 15996-16003) generated fibrils that were visible by eye and that were large enough to be separated from solution by centrifugation at 13,000 x g for 4 min. With high concentrations of enzyme, the pC-collagen was completely cleaved in 1 h, and turbidity was near maximal in 3 h, but collagen continued to be incorporated in fibrils for over 10 h. Because the pC-collagen was uniformly labeled with 14C-aminoacids, the concentration of soluble collagen and, therefore, the critical concentration of polymerization were determined directly. The critical concentration was independent of the initial pC-collagen concentration and of the rate of cleavage. The critical concentration decreased with temperature between 29 and 41 degrees C and was 0.12 +/- 0.06 (S.E.) microgram.ml-1 at 41 degrees C. The thermodynamic parameters of assembly were essentially independent of temperature in the range 29 to 41 degrees C. The process was endothermic with a delta H value of +56 kcal.mol-1, but entropy driven with a delta S value of +220 cal.K-1.mol-1. The Gibbs energy change for polymerization was -13 kcal.mol-1 at 37 degrees C. The data demonstrate, for the first time, that type I collagen fibril formation de novo is a classical example of an entropy-driven self-assembly process similar to the polymerization of actin, flagella, and tobacco mosaic virus protein.     

Inhibition of in vitro human chorionic gonadotropin-stimulated testosterone production in testis and of ovulation in the rat by charcoal-treated rat testicular extract

Previously, we described the presence of a factor obtained from a 105,000 X g supernatant of rat testis that was found to inhibit human chorionic gonadotropin (hCG) binding to gonadal receptors. In the present study, similarly prepared testicular extract was tested for its effects on in vitro hCG-stimulated testosterone production by isolated testis interstitial cells and for its effect on spontaneous ovulation in the rat. Incubation of interstitial cells with charcoal-treated extract significantly inhibited the steroidogenic response to hCG in a dose-related manner. This inhibition was also apparent after heating the extract for 10 min at 100 degrees C. Preincubation of the cells with charcoal-treated extract resulted in an inhibitory effect that was not readily reversed by subsequent addition of hCG, revealing an element of irreversibility in the mechanism of inhibition. A single i.p. injection of testicular extract given between 1430-1630 h of proestrus inhibited spontaneous ovulation in the rat. This effect was also observed after heating the extract for 10 min at 100 degrees C; in contrast, no significant effect was obtained with the injection of a similar dose of liver extract. Administration of 5 IU hCG after pretreatment with the testicular extract did not reverse the inhibitory effect on ovulation, indicating that this effect was probably not exerted at the hypothalamus-pituitary level. It is concluded that the aqueous testicular extract contains a factor able to antagonize the physiological events mediated by luteinizing hormone (LH)/hCG, and that this factor is consistent with the presence of an LH/hCG-binding inhibitory activity in rat testis.     

Subunit exchange demonstrates a differential chaperone activity of calf alpha-crystallin toward beta LOW- and individual gamma-crystallins

The chaperone activity of native alpha-crystallins toward beta(LOW)- and various gamma-crystallins at the onset of their denaturation, 60 and 66 degrees C, respectively, was studied at high and low crystallin concentrations using small angle x-ray scattering (SAXS) and fluorescence energy transfer (FRET). The crystallins were from calf lenses except for one recombinant human gamma S. SAXS data demonstrated an irreversible doubling in molecular weight and a corresponding increase in size of alpha-crystallins at temperatures above 60 degrees C. Further increase is observed at 66 degrees C. More subtle conformational changes accompanied the increase in size as shown by changes in environments around tryptophan and cysteine residues. These alpha-crystallin temperature-induced modifications were found necessary to allow for the association with beta(LOW)- and gamma-crystallins to occur. FRET experiments using IAEDANS (iodoacetylaminoethylaminonaphthalene sulfonic acid)- and IAF (iodoacetamidofluorescein)-labeled subunits showed that the heat-modified alpha-crystallins retained their ability to exchange subunits and that, at 37 degrees C, the rate of exchange was increased depending upon the temperature of incubation, 60 or 66 degrees C. Association with beta(LOW)- (60 degrees C) or various gamma-crystallins (66 degrees C) resulted at 37 degrees C in decreased subunit exchange in proportion to bound ligands. Therefore, beta(LOW)- and gamma-crystallins were compared for their capacity to associate with alpha-crystallins and inhibit subunit exchange. Quite unexpectedly for a highly conserved protein family, differences were observed between the individual gamma-crystallin family members. The strongest effect was observed for gamma S, followed by h gamma Srec, gamma E, gamma A-F, gamma D, gamma B. Moreover, fluorescence properties of alpha-crystallins in the presence of bound beta(LOW)-and gamma-crystallins indicated that the formation of beta(LOW)/alpha- or gamma/alpha-crystallin complexes involved various binding sites. The changes in subunit exchange associated with the chaperone properties of alpha-crystallins toward the other lens crystallins demonstrate the dynamic character of the heat-activated alpha-crystallin structure.     

Isolation and characterization of pepsin-treated type III collagen from calf skin.

Calf skin collagen was solubilized by incubating acid-extracted calf skin with pepsin at pH 2.0 and 25 degrees C, conditions that did not cause degradation of the triple helical region of collagen. Type III collagen was separated from type I collagen by differential salt precipitation at pH 7.5. The isolated type III collagen contained mainly gamma and higher molecular weight components cross-linked by reducible and/or non-reducible bonds. The isolated alpha1 (III) chains had an amino acid composition characteristic of type III collagen. Denatured but unreduced type III collagen, chromatographed on carboxymethyl-cellulose, eluted in the alpha 2 region, while after reduction and alkylation the alpha1 (III) chains eluted between the positions of alpha1 (I) and alpha2. The mid-point melting temperature temperature (tm) of type III collagen (35.1 degrees C) in a citrate buffer at pH 3.7 was somewhat lower than that of type I collagen (35.9 degrees C). Renaturation experiments at 25 degrees C showed that denatured type III collagen molecules with intact intramolecular disulfide bridges (gamma components) reform the triple helical structure of collagen much faster than reduced and carboxymethylated alpha1 (III) chains.     

The immune response of tilapia Oreochromis mossambicus and its susceptibility to Streptococcus iniae under stress in low and high temperatures

Mozambique tilapia Oreochromis mossambicus acclimated to 27 degrees C were then held at 19, 23, 27 (control), 31 and 35 degrees C, and were examined for non-specific cellular and humoral responses after 12-96 h. Total leucocyte count decreased significantly when fish were transferred to 19 and 23 degrees C after 48 and 96 h, and when transferred to 35 degrees C over 12-96 h, respectively. Respiratory burst decreased significantly when fish were transferred to 19, 31 and 35 degrees C over 24-96 h, whereas phagocytic activity and phagocytic index decreased significantly when fish were transferred to low temperatures (19 and 23 degrees C) and high temperatures (31 and 35 degrees C) over 12-96 h. Lysozyme activity decreased significantly when fish were transferred to 19 degrees C after 12-96 h, but increased significantly when transferred to 31 and 35 degrees C over 48-96 h. Alternative complement pathway (ACH(50)) also decreased significantly when transferred to 19 and 23 degrees C after 12h, but increased significantly when transferred to 31 and 35 degrees C after 24h. In another experiment, tilapia reared at 27 degrees C were injected intraperitoneally with Streptococcus iniae at a dose of 1 x 10(7)colony-forming units (cfu)fish(-1), and then reared onward at water temperatures of 19, 23, 27 (control), 31 and 35 degrees C. Over 48-168 h, the cumulative mortality of S. iniae-injected fish held in 19 and 35 degrees C was significantly higher than that of injected-fish held in 23, 27 and 31 degrees C. It is concluded that transfer of tilapia O. mossambicus from 27 degrees C to low temperatures (19 and 23 degrees C) after 12h, and transfer of fish from 27 degrees C to high temperatures (31 and 35 degrees C) reduced their immune capability. Moreover, tilapia under temperature stress at 19 and 35 degrees C from 27 degrees C decreased its resistance against S. iniae.